Emotion
Emotion, in its most general definition, is a neural impulse that moves an organism to action, prompting automatic reactive behavior that has been adapted through evolution as a survival mechanism to meet a survival need. Linda Davidoff defines emotion as a feeling that is expressed through physiological functions such as facial expressions, faster heartbeat, and behaviors such as aggression, crying, or covering the face with hands. Based on discoveries made through neural mapping of the limbic system, the neurobiological explanation of human emotion is that emotion is a pleasant or unpleasant mental state organized in the limbic system of the mammalian brain.
Defined as such, these emotional states are specific manifestations of non-verbally expressed feelings of agreement, amusement, anger, certainty, control, disagreement, disgust, disliking, embarrassment, fear, guilt, happiness, hate, interest, liking, love, sadness, shame, surprise, and uncertainty. If distinguished from reactive responses of reptiles, emotions would then be mammalian elaborations of general vertebrate arousal patterns, in which neurochemicals (e.g., dopamine, noradrenaline, and serotonin) step-up or step-down the brain's activity level, as visible in body movements, gestures, and postures. In mammals, primates, and human beings, feelings are displayed as emotion cues.
For example, the human emotion of love is proposed to have evolved from paleocircuits of the mammalian brain (specifically, modules of the cingulated gyrus) designed for the care, feeding, and grooming of offspring.